A prior art impact crushing process is carried out in several stages. At the first stage, the impact tool, or hammer, of the crusher strikes the lumps of feedstock entering the crushing chamber. Each of the lumps subjected to a primary impact force is broken up partially and thrown against a deflecting member at a definite velocity. At the second stage, a lump striking the deflecting element is subjected to a secondary impact force, which crushes the lump to a definite size. In a simple case, one deflecting member is used, in which case a lump is crushed in two stages, though the crushing result is minimal.
The deflecting members, which are arranged in succession one after another are metal plates, grid bars, rods, bars, or screens.
Three or four deflecting members, less frequently more than five members, are installed to improve the efficiency of crushing. In this case, a lump is crushed in an average of four to six stages.
From the viewpoint of energy transmission, impact against a stationary barrier has the weakest effect possible (ref. E. V. Alexandrov and V. V. Sokolinsky, "Applied Theory and Calculation of Impact Systems", Nedra Publishers, Moscow, 1969, p.p. 15 to 17).
The above-described process has a low crushing effect since the surface of the deflecting member has a single function, directing lumps of feed material back to the impact members of the primary crushing rotor. In this case, the energy of the deflecting member itself is not utilized.
Also widely used in the art are centrifugal impact crushers, in which rock lumps are engaged by an acceleration rotor or disk and imparted a considerable velocity of up to 100 or 120 m/sec. The centrifugal force throws the lumps against a barrier which is designed as a ring mounted fixedly or rotatably about a common center of rotation.
The impact of the rock lumps against the annular barrier and the pattern of subsequent crushing do not actually differ from the conventional impact crushing process. Furthermore, this process is characterized by considerable specific consumption and inefficient use of electric power.
Another prior art crusher comprises two horizontal rotors of the AP-CM type (ref., for example, prospectus of the Holmes Hazemag firm, Roots Division of Dresser Holmes, Ltd.).
The rotors are arranged one above the other in the crusher so that the line connecting the axes of rotation of the rotors is inclined to the horizontal plane at a certain angle. In this crusher, rock lumps are crushed successively by the primary crushing rotor, and then by the deflecting members provided along the periphery thereof, and finally further crushed by the secondary crushing rotor which is also provided with fixed or spring-biased deflecting members arranged along the periphery thereof. The crushing process is carried out in six to eight stages. To increase the frequency of collisions, one of the rotors is provided with six hammers.
This crusher has all the drawbacks indicated above, that is, considerable power consumption and low efficiency.
Yet another prior art impact crusher (ref., for example, French Patent No. 2,091, 446, 1972) comprises two rotors, the axes of which lie in a plane extending at an angle to the horizon and the rotors themselves are positioned one above the other. The rotors rotate in opposite directions. Both rotors crush the rock successively and are provided with fixed deflecting members as well. The crusher has a large overall height, is inconvenient to operate, and requires much power and metal.
A further prior art impact crusher comprises a housing having a primary crushing rotor secured therein, with two secondary crushing rotors and a charging hole provided above it, the housing wall serving as a feed chute to deliver rock and ore lumps to the primary crushing rotor, with a discharging hole provided beneath it (ref., for example, USSR Inventor's Certificate No. 183,053).
This crusher performs a process for impact crushing of rock and ore lumps, comprising subjecting a rock lump first to a primary impact force that causes the lump to break up into a plurality of smaller pieces which are then subjected to a secondary impact force having a stochastic force vector distribution profile.
In operation, the material to be crushed is directed to the primary crushing rotor and then thrown against the hammers of the secondary crushing rotors. In this crusher, the hammers of the secondary crushing rotors are used as the deflecting members.
Rock lumps are crushed in three stages. At the first stage, crushing occurs as the material is engaged by the primary crushing rotor hammers. At the second stage, the material is crushed as it is engaged by the secondary crushing rotor hammers. At the third stage, the lumps are finally broken up against the grid bars.
This crusher helps to slightly improve the efficiency of crushing and the quality of material. However, it, too, has a number of drawbacks, the principal of which are as follows:
stochastic pattern of rock lump crushing because the arrangement and operation of all the rotors are not synchronized in time; PA1 the impact force delivered by the secondary crushing rotor to the lump has a low efficiency because the rotor has a low speed of rotation, but essentially because a direct central impact cannot be delivered; PA1 the mass of the secondary crushing rotors performing deflecting functions is focused in their centers, for which reason the disintegrating effect of the rotors cannot be utilized in full; and PA1 the arrangement of the primary and secondary crushing rotors on a vertical axis reduces the possibility of crusher efficiency being improved, increases the overall dimensions of the crusher and raises labor inputs for operation and maintenance.